package demo02;
//矩阵区域和
class Solution {
    public int[][] matrixBlockSum(int[][] mat, int k) {
        int m = mat.length;
        int n = mat[0].length;
        int[][] dp = new int[m + 1][n + 1];
        //存dp表
        for(int i = 1;i <= m;i++)
            for(int j = 1;j <= n;j++){
                dp[i][j] = dp[i-1][j]+dp[i][j-1]-dp[i-1][j-1]+mat[i-1][j-1];
            }
        //存ans表
        int[][] ans = new int[m][n];
        for(int i = 0;i < m;i++)
            for(int j = 0;j < n;j++){
                int x1 = Math.max(0,i - k )+1;
                int y1 = Math.max(0,j - k )+1;
                int x2 = Math.min(m-1,i + k )+1;
                int y2 = Math.min(n-1,j + k)+1;
                ans[i][j] = dp[x2][y2]-dp[x2][y1-1]-dp[x1-1][y2] + dp[x1-1][y1-1];
            }
        return ans;
    }
}